Modern gas turbine engines can be extremely compact, with temperature sensitive components such as turbine rotor bearings placed in close proximity to the turbine section in some designs. This has necessitated the use of shielding for protection, which shielding is positioned between the hot combustion gases and the critical components.
Also, in a high performance gas turbine engine, it is of prime importance that the heat shield maintain a minimal clearance from the turbine impeller to minimize flow of heated air behind the backface of the turbine, which adversely affects efficiency of the engine. Typical flat heat shields positioned adjacent the backface of the turbine require substantial spacing from the turbine as a result of "flowering" or "bending" of the turbine tip during engine operation. Spacing of up to 0.90 inch may be required to allow space for such flowering as well as axial movement of the turbine. This spacing results in substantial airflow along the backface of the impeller, thereby adversely affecting engine efficiency.
For example, in a prior art radial inflow turbine engine such as that shown in FIG. 2, a heat shield is implemented. The heat shield 3 is positioned against the backface 4 of the rotatable turbine 5. The heat shield 3 may be flat or contoured to match the backface 4 of the turbine rotor. The shroud 6 and turbine tip 7 cooperate to form a tip clearance gap 8 which is approximately 0.020 inch. This gap 8 allows flow of heated air along the backface 4 of the turbine 5, which causes losses in efficiency.
It is therefore desirable to provide a heat shield for a turbine engine which efficiently shields sensitive components while minimizing flow of air along the backface of the turbine.